The cationic antimicrobial peptides are promissory candidates, as new potential antibiotics, with clinical utility. These peptides are produced by both prokaryotic and eukaryotic organisms (Saberwal G., Nagaraj R. 1994. Cell-lytic and antibacterial peptides that act by perturbing the barrier function of membranes: facets of their conformational features, structure-function correlations and membrane-perturbing abilities. Biochim. Biophys. Acta. 1197: 109–131; 1. Boman H. G. 1995. Peptide antibiotics and their Role in innate immunity. Annu. Rev. Immunol. 13: 61–92; Nicolas P., Mor A. (1995). Peptides as weapons against microorganisms in the chemical defense system of vertebrates. Annu. Rev. Microbiol. 4: 277–304; and Maloy W. L., Kari U. P. 1995. Structure-activity studies on magainins and other host defense peptides. Biopolymers 37: 105–122). It is known that they are an essential component of the defense system of vertebrates and invertebrates, which are destined to control the cellular multiplication and the invasion of microbial pathogens in organs and tissues (Ganz T. 2002. Antimicrobial peptides in host defense of the respiratory track. J. Clin. Inv. 109: 693–697). In view of their therapeutical potential, these natural antibiotics have been the subject matter of many studies in recent years (Hancock R. E. W. and Chapple D. 1999. Peptides antibiotics. Antimicrob. Agents Chemother. 43: 1317–1323). The antimicrobial activity of the cationic peptides has been mainly attributed to the disturbance of the cytoplasmic membrane or to the effector function in the natural immunity. The three-dimensional structure of these peptides are highly conserved in spite of the fact that the primary structure is very heterologous (Maloy and Kari 1995, cited article; Hancock R. E. W. 2001. Cationic peptides: effectors in innate immunity and novel antimicrobials. The Lancet infectious diseases. 1: 156–164.). These peptides are folded, either forming disulphide bridges or by means of the contact with the lipids of the biological membranes (Bernheimer A. W. 1986. Interactions between membranes and cytolytic peptides. Biochim. Biophys. Acta. 864: 123–141.), in an amphiphilic three-dimensional structure wherein the positive charges and the hydrophilic domain are separated from the hydrophobic domain (Hancock, 2001, cited article) leading to the formation of pores with variable selectivity on the membranes of bacteria or eukaryotic cells. The damage of the plasmatic membrane in many cases produces the cellular lysing. Examples of these damages are in U.S. Pat. No. 4,355,104 (October, 1982) and U.S. Pat. No. 4,520,016 (May, 1985) by Hultmark et al., who describe the bacteriolytic properties of some cecropins against Gram-negative bacteria. A very interesting aspect is that the cecropins described in the above patents by Hultmark et al., are not universally effective against all Gram-negative bacteria. For example, the cecropins described lyse bacterium Serratia marcescens strain D61108, but not Serratia marcescens strain D611. Furthermore, it has been reported that the cecropins do not have lytic activity against eukaryotic cells such as insect cells, liver cells and sheep erythrocytes, as it is observed in the patents by Hultmark and Zasloff U.S. Pat. No. 4,810,777 (March 1989); and in Steiner et al., (Steiner H., Hultmark D., Engstrom A., Bennich H., Boman H. G. 1981. Sequence and specificity of two antibacterial proteins involved in insect immunity. Nature. 292: 246–248), Andreu et al., (Andreu D., Merrifield R. B., Steiner H., Boman H. G. 1985. N-terminal analogues of cecropin A: synthesis, antibacterial activity, and conformational properties. Biochemistry. 24: 1683–1688.) and Boman et al., (Boman H. G., Faye I., von Hofsten P., Kockum K., Lee J. Y., Xanthopoulos K. G., Bennich H., Engstrom A., Merrifield R. B., Andreu D. 1985. On the primary structures of lysozyme, cecropins and attacins from Hyalophora cecropia. Dev. Comp. Immunol. 9: 551–558.). More recently, a group of antimicrobial peptides produced by human tissues and known as defensins has been reported in the patents by Barra, et al., U.S. Pat. No. 6,310,176 (October 2001), and Olsen et al., U.S. Pat. No. 6,420,116 (July 2002).
Other peptides with the same properties are naturally produced in the immunological system of the insects Sarcophaga peregrina and Bombyx mori, as they were reported by Nakajima et al. (Nakajima Y., Qu X. M., Natori S. 1987. Interaction between liposomes and sarcotoxin IA, a potent antibacterial protein of Sarcophaga peregrina (flesh fly). J. Biol. Chem. 262: 1665–9). The differences in the bacteriolytic activity of the antimicrobial peptides have been attributed to the differences in the composition of the cell plasma membranes (Bernheimer, 1986, cited article). Therefore, it is not surprising that less specific peptides such as the cecropins have more capacity for lysing prokaryotic cells than the eukaryotic cells of the insect.